1. Field in the Invention
The present invention relates generally to an unmanned vehicle control system and the method, and more specifically to steering device control system and the method incorporated with the unmanned vehicle control system. The unmanned vehicle is a forklift truck, for instance, which is automatically remote-controlled so as to travel along a fixed guide line in response to various command signals transmitted from a fixed host computer. The unmanned vehicle is used for conveying material, semi-finished products, etc. in an unmanned factory, warehouse, etc, for instance.
2. Description of the Prior Art
In general, an unmanned vehicle is driven along fixed guide lines. An alternating current having an appropriate frequency (e.g. 10 kc) is passed through the guide lines to generate a magnetic field near the guide lines. A pair of magnetic field detecting coils are disposed symmetrically with respect to the longitudinal axis of the vehicle body in order to detect a vehicle offset produced when the vehicle skews or is misaligned away from the guide line. To detect vehicle offsets (misalignment) from the guide line, the difference in magnetic field intensity between the two symmetrically-arranged coils is detected. In response to the detected difference signal indicative of vehicle offset, a steering device mounted on the vehicle is actuated by a steering motor in the direction that a detected offset may be reduced into within a dead zone (offset is no longer adjusted). The speed of the steering DC motor can be adjusted by a chopper circuit. The chopper circuit can generate a chopped current the duty ratio of which is freely adjustable by controlling the inputs of the chopper circuit.
Conventionally, however, the offset signals detected by the offset detecting coils are feedbacked to a steering motor control section including the steering motor driving chopper circuit and a chopper controller (microcomputer). Since the main microcomputer is mounted on the vehicle in order to implement various controls other than steering device control, it is rather wasteful or redundant to additionally provide the chopper controller from economical or energy saving standpoint. Further, since the feedback signal is applied to the chopper controller, it is impossible for the main computer to directly self-diagnose the steering device including the steering motor, steering motor chopper circuit, etc.
Further, in the prior-art steering device control system, the speed of steering motor is simply controlled according to the magnitude of detected offset value. In more detail, when the detected offset value is great, the steering DC motor is driven quickly by simply increasing the duty ratio of current supplied from the chopper circuit to the steering motor; when the detected offset value is small, the steering DC motor is driven slowly by simply decreasing the duty ratio of current supplied from the chopper circuit to the steering motor. Therefore, there exists a problem in that the vehicle easily skews away from the guide line beyond control; that is, it is impossible to stably correct the steering misalignment at high response speed, in particular when the vehicle is travelling at relatively high speed.